An envelope for a cathode ray tube, especially the panel or face plate thereof.
A cathode ray tube customarily has a glass envelope which is evacuated and hermetically sealed for tube operation. The envelope comprises a viewing panel member, a funnel member and a tubular neck member. An electron gun is mounted in the neck member.
The panel member is often referred to as a face plate, or a display window, since it provides a screen on which a picture or display is formed. Normally, the panel member has a depending, peripheral skirt that is sealed to the funnel member with a fused sealing material.
Since a tube operates in an evacuated state, there is a pressure difference of one atmosphere across the panel. This creates a risk of implosion when flaws develop as the glass cools, or are caused by scuffs or scratches during handling. To counter this, the panel thickness is increased. Normally, glass thickness in the panel is greater than that in the funnel and neck member, since these members are less prone to damage and are not exposed during tube operation.
The ever increasing demand for larger picture tube size has led to larger and larger panels. Coincident therewith has been the increase in panel and tube weight. This has led to difficulty in handling the heavy ware without damage. It has also entailed longer times and more energy to process the panel and the tube, thus adding to the cost. This has led to a strenuous search for an alternative to increased panel thickness as a protection against implosion.
Numerous proposals have been made to use a so-called implosion protection band. Such a band tightly encircles the skirt portion of the panel, and may be adherently sealed thereto. The protection band may be composed of metal or other strong materials.
It is also known to strengthen glass by tempering. This practice is commonly employed for such diverse items as automotive glazing and glass cookware. Glass may be thermally tempered by blowing cooling air on the surface. This accelerates setting of the surface glass, thereby inducing compressive stresses therein. An alternative practice, chemical tempering, has been proposed. In this procedure, ion exchange is employed to create compression by crowding ions in the glass surface.
The present invention is directed to producing an improved envelope for a cathode ray tube. In particular, it is directed to the production of larger sized tubes in excess of a 19xe2x80x3 panel dimension. It is further directed at minimizing the glass thickness in a cathode ray tube (CRT) panel while maintaining full protection against implosion. It is also directed to a method of producing a panel for a cathode ray tube that has minimum thickness consistent with full protection against implosion.
The article of the invention is a glass envelope for a cathode ray tube comprising a panel member having a thickness (t) defined by the equation:
("sgr")P=kP(a/t)2
wherein ("sgr")P is the net tensile stress in the panel, (a) is one half the length of the minor axis in inches, (t) is the panel thickness in inches, (P) is atmospheric pressure in psi and (k) is a structural constant based on tube geometry. The panel has a net tensile stress not exceeding 1150 psi, a surface compression induced during panel manufacture, and an implosion protection band shrink-fitted around a skirt on the panel that augments surface compression in the panel, whereby the panel thickness is substantially less than that of a corresponding untreated tube envelope.
The invention further resides in a method of reducing the thickness of a panel member in a cathode ray tube glass envelope wherein the thickness (t) is defined by the equation ("sgr")P=kP(a/t)2 wherein ("sgr")P is the maximum tensile stress in the panel, the method comprising imparting compression in the panel surface by treatment of the surface, and augmenting this compression by shrink-fitting an implosion protecting band about a skirt on the panel, while maintaining the value of ("sgr")P at not over 1150 psi, thereby permitting a reduction in panel thickness from that in an untreated panel.
Literature of possible interest is listed on an attached document.